Frame transmission system and method of interference alignment and controlling in multi-cell random access network

ABSTRACT

Provided is a frame transmission method of interference alignment (IA) and controlling, the method including calculating a channel matrix of a basic service set (BSS) by measuring channel information between an access point and a user terminal, performing singular value decomposition (SVD) based on the calculated channel matrix, selecting a beamforming vector in consideration of an interference amount associated with another access point based on the SVD performed by the channel matrix, and calculating a leakage interference (LIF) value based on the selected beamforming vector.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Korean PatentApplication No. 10-2014-0075601, filed on Jun. 20, 2014, and KoreanPatent Application No. 10-2015-0025000, filed on Feb. 23, 2015, in theKorean Intellectual Property Office, the disclosure of which isincorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a method of controlling interferencebetween multi-cells in a random access network, and more particularly,to a technical idea of accessing a beamforming and a channel based onchannel information obtained in a distributed manner in the randomaccess network.

2. Description of the Related Art

Since users increasingly converge on a small space and mobile datatraffic is gradually increasing, extensive interference among the usersin a wireless communication network may be generated. Accordingly, aneffective communication by the users may place a high priority oncontrolling an interference that degrades a network performance. Achannel in which the interference among the users is present may bereferred to as an interference channel. The simplest method of removingthe interference from the interference channel is the users utilizinglimited communication resources without sharing, for example, a time, afrequency, and an antenna. A time division multiple access (TDMA) todivide and use a time, or a frequency division multiple access (FDMA) todivide and use a frequency may be included in the foregoing method.However, since the method supports communication for a single user at atime, spectral efficiency is substantially low. Thus, multiple users mayneed to simultaneously use the communication resources in order toenhance system performance. Conducting research on interference channelsand finding an optimal interference control scheme may be significant toenhance efficiency in communication.

Recently, based on an information theory, a new scheme, for example, aninterference alignment (IA), may obtain a multiplexing gain enhancedwhen compared to conventional technology. In a case of a current IAscheme, issues, such as a calculation complexity required for eachterminal and information on a wireless channel to be provided in advancemay occur in practice.

Accordingly, to implement the IA scheme in an actual system, signalingoverhead among geometrically increasing nodes may be required. Therequirement of signaling overhead may be a greatest factor hinderingactual implementation. Therefore, technology for solving an issue of therequirement of signaling overhead and maximizing a performance gain ofthe IA in a random access network may be required.

Recently, in a cellular system, an opportunistic interference alignment(OIA) scheme to reduce the signaling overhead is proposed. Through theOIA scheme, beamforming may be implemented to allow users to minimizeinterference in another cell based on restricted channel information andthus, a base station may be allowed to select a user corresponding to aleast amount of interference in another cell, in a cell of the basestation. The selection may be available in the cellular system. However,a direct application of the OIA may have an issue since a centralizedcontroller, such as a base station, is not a basic element of the randomaccess system.

SUMMARY

According to an aspect of the present invention, there is provided aframe transmission method of interference alignment (IA) andcontrolling, the method including verifying channel informationassociated with an adjacent channel, receiving a receiving vector froman access point of the adjacent channel, calculating an effectivechannel matrix using the verified channel information and the receivedreceiving vector, measuring an interference amount based on thecalculated effective channel matrix, and selecting a user terminal towhich transmission is to be directed based on the measured interferenceamount.

The calculating may include calculating the effective channel matrix bymeasuring the channel information including a sounding frame or a beaconframe periodically transmitted to the user terminal from the accesspoint.

The calculating may include transmitting desired signal spaceinformation including a null space and interference space informationrandomly generated for IA to the user terminal through the soundingframe or the beacon frame, wherein the interference space information isinformation associated with an interference space allowing interferencefrom user terminals in different cells, and the desired signal spaceinformation is information associated with a space set by the accesspoint to receive a signal.

According to another aspect of the present invention, there is provideda frame transmission method of IA and controlling, the method includingcalculating a channel matrix of a basic service set (BSS) by measuringchannel information between an access point and a user terminal,performing singular value decomposition (SVD) based on the calculatedchannel matrix, selecting a beamforming vector in consideration of aninterference amount associated with another access point based on theSVD performed by the channel matrix, and calculating a leakageinterference (LIF) value based on the selected beamforming vector.

The selecting of the beamforming vector may include selecting abeamforming vector of which the interference amount associated withanother access point is a minimum.

According to still another aspect of the present invention, there isprovided a frame transmission method of IA and controlling, the methodincluding receiving a contention window (CW) value broadcasted by anaccess point, setting a backoff counter based on the received CW value,and generating a LIF value related to an access point monitored for apredetermined period of time and performing a backoff by setting thebackoff counter when a channel is in an idle state.

The performing of the backoff may include dividing a range of cumulativedistribution function (CDF) values based on the CW value, calculatingthe LIF value based on a channel condition during a transmissionattempt, calculating the CDF values corresponding to the calculated LIFvalue, and selecting the backoff counter based on the calculated CDFvalues.

The backoff counter may be selected according to a channelcharacteristic based on the LIF value and determined to be a valuebetween 1 and the CW value.

The frame transmission method of IA and controlling may further includedecreasing the selected backoff counter by 1 for each backoff slot andattempting a packet transmission through a user terminal of which thebackoff counter is to be 0.

The frame transmission method of IA and controlling may further includedecreasing the backoff counter for each backoff slot and suspending thebackoff when a user terminal attempts a packet transmission.

The CW value may be set at the access point based on a first throughputobtained from a packet that arrives in a desired signal space and asecond throughput to be obtained through a multiple-packet recoveryusing a user terminal performing simultaneous transmissions throughout asystem.

The CW value may be set as a constant based on a reciprocal value tomaximize a sum of the first throughput and the second throughput.

According to a further aspect of the present invention, there isprovided a frame transmission method of IA and controlling, the methodincluding verifying a number of users attempting simultaneoustransmissions in different cells, comparing the verified number of usersto a number of antennas at an access point, and setting, based on aresult of the comparing, to receive a stream in a multiple-packet schemewhen the number of antennas at the access point is less than theverified number of users.

The frame transmission method of IA and controlling may further includedetermining whether multiple users attempt the simultaneoustransmissions, and the verifying may include verifying the number ofperforming the simultaneous transmissions in the different cells whenthe multiple users attempt the simultaneous transmissions.

According to still another aspect of the present invention, there isprovided a frame transmission system of IA and controlling, the systemincluding a calculator configured to calculate a channel matrix of a BSSby measuring channel information between an access point and a userterminal, a processor configured to perform SVD based on the calculatedchannel matrix, and a selector configured to select a beamforming vectorin consideration of an interference amount associated with anotheraccess point based on the SVD performed by the channel matrix, whereinthe calculator may calculate an LIF value based on the selectedbeamforming vector.

The calculator may calculate the channel matrix by measuring the channelinformation including a sounding frame or a beacon frame periodicallytransmitted to the user terminal from the access point.

The calculator may transmit desired signal space information including anull space and interference space information randomly generated for IAto the user terminal through the sounding frame or the beacon frame,wherein the interference space information may be information associatedwith an interference space allowing interference from user terminals indifferent cells, and the desired signal space information may beinformation associated with a space set by the access point to receive asignal.

According to yet another aspect of the present invention, there isprovided a frame transmission system of IA and controlling, the systemincluding a receiver configured to receive a CW value broadcasted by anaccess point, a setter configured to set a backoff counter based on thereceived CW value, and a processor configured to generate an LIF valuerelated to an access point monitored for a predetermined period of timeand perform a backoff by setting the backoff counter when a channel isin an idle state.

The processor may divide a range of CDF values based on the CW value,calculate the LIF value based on a channel condition during atransmission attempt, calculate the CDF values corresponding to thecalculated LIF value, and select the backoff counter based on thecalculated CDF values.

According to further another aspect of the present invention, there isprovided a frame transmission system of IA and controlling, the systemincluding a counter configured to verify a number of users performingsimultaneous transmissions in different cells, a comparer configured tocompare the verified number of users to a number of antennas at theaccess point, and a setter configured to set, based on the result of thecomparing, to receive a stream in a multiple-packet scheme when thenumber of antennas at the access point is less than the verified numberof users.

The frame transmission system of IA and controlling may further includea determiner configured to determine whether multiple users attempt thesimultaneous transmissions, wherein the counter may verify the number ofusers performing simultaneous transmissions in different cells when themultiple users attempt the simultaneous transmissions.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects, features, and advantages of the inventionwill become apparent and more readily appreciated from the followingdescription of exemplary embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1 is a diagram illustrating a multi-cell random access networkaccording to an embodiment of the present invention;

FIG. 2 is a flowchart illustrating a frame transmission method ofinterference alignment (IA) and controlling through a beamforming methodbased on a singular value decomposition (SVD) according to an embodimentof the present invention;

FIG. 3 is a flowchart illustrating a frame transmission method of IA andcontrolling through a backoff method for a channel access according toan embodiment of the present invention;

FIG. 4 is a diagram illustrating a cumulative distribution function(CDF) values associated with a leakage interference (LIF) value and acontention window (CW) value according to an embodiment of the presentinvention;

FIG. 5 is a flowchart illustrating a frame transmission method of IA andcontrolling through a stream reception method at an access pointaccording to an embodiment of the present invention;

FIG. 6 is a block diagram illustrating a frame transmission system of anIA and controlling using a beamforming based on SVD according to anembodiment of the present invention.

FIG. 7 is a block diagram illustrating a frame transmission system of IAand controlling using a backoff for a channel access according to anembodiment of the present invention; and

FIG. 8 is a block diagram illustrating a frame transmission system of IAand controlling using a stream reception at an access point according toan embodiment of the present invention.

DETAILED DESCRIPTION

Hereinafter, example embodiments of the present invention will bedescribed with reference to the drawings.

When it is determined a detailed description related to a related knownfunction or configuration they may make the purpose of the presentinvention unnecessarily ambiguous in describing the present invention,the detailed description will be omitted here. Also, terminologies usedherein are defined to appropriately describe the exemplary embodimentsof the present invention and thus may be changed depending on a user,the intent of an operator, or a custom. Accordingly, the terminologiesmust be defined based on the following overall description of thisspecification. Like reference numerals refer to like elementsthroughout.

FIG. 1 is a diagram illustrating a multi-cell random access network 100according to an embodiment of the present invention.

The multi-cell random access network 100 includes multiple users andmultiple access points distributed in an area.

Each of the access points may communicate with the multiple users. FIG.1 is a diagram illustrating a system scenario implemented by themultiple access points and the multiple users, and the users maycommunicate with the corresponding access points. The correspondingaccess points and the users may include a single cell and a basicservice set (BSS). A network topology in which individual BSSs overlapmay be referred to as an overlapping cell or an overlapping basicservice set (OBBS). The access points and user terminals may be equippedwith multiple antennas and the user terminals may process a channelaccess for a communication with the access points based on a randomaccess scheme.

To implement an interference alignment (IA) scheme in an actual system,signaling overhead among geometrically increasing nodes may be needed.The need for the signaling overhead may be a greatest factor hinderingan actual implementation. The present disclosure may effectively solvean issue of needing the signaling overhead and maximize a performancegain of the IA in a random access network.

The present disclosure may perform the IA and controlling to implementbeamforming of a user to minimize interference amount to a cell or anaccess point, and perform backoff of users for a multiple user channelaccess.

The present disclosure may also provide an optimal contention window(CW) value based on a backoff algorithm for the IA and controlling, andallow the multiple users to receive a multi stream from an access pointwhen a simultaneous transmission is performed.

A frame transmission method of IA and controlling may verify channelinformation associated with an adjacent channel and receive a receivingvector from an access point of the adjacent channel.

An effective channel matrix may be calculated using the verified channelinformation and the received receiving vector and an interference amountmay be measured based on the calculated effective channel matrix.

In an example, to calculate the effective channel matrix, channelinformation including a sounding frame or a beacon frame periodicallytransmitted to a user terminal from an access point may be measured.Also, desired signal space information including a null space andinterference space information randomly generated for an IA may betransmitted to the user terminal through the sounding frame and thebeacon frame. The interference space information corresponds toinformation associated with an interference space allowing interferencefrom user terminals in different cells and the desired signal spaceinformation corresponds to information associated with a space set bythe access point to receive a signal.

Hereinafter, the frame transmission method of IA and controlling mayperform the IA and controlling by selecting a user terminal to whichtransmission is to be directed based on the measured interferenceamount.

FIG. 2 is a flowchart illustrating a frame transmission method of IA andcontrolling through a beamforming method based on a singular valuedecomposition (SVD) according to an embodiment of the present invention.

In operation 201, the frame transmission method of IA and controllingthrough the beamforming method based on the SVD may calculate a channelmatrix of a BSS by measuring channel information between an access pointand a user terminal.

Each of the access points may allow a user terminal to measure channelinformation between the user and the access point by periodicallytransmitting a sounding frame and a beacon frame.

The access point using multiple antennas includes a space in which anumber of data streams corresponding to a number of antennas are to besimultaneously received. A portion of the space may be used as a desiredsignal space and the remaining space may be used as an interferencespace. The interference space corresponds to a space allowinginterference from the user terminals in different cells and the desiredsignal space corresponds to a space set by the access point to receive asignal. The user terminals in different cells may minimize a number ofsignals directed to the desired signal space. Related information may bestored in the beacon frame.

An example of beamforming based on SVD may be described as shown below.

K cells may coexist, each access point may include M antennas, and eachuser terminal may include L antennas. Each access point may supportsimultaneous transmission of S(≦M) streams through an uplink. A size ofthe desired signal space is denoted as S. Each user terminal maytransmit a stream. A channel matrix from a user terminal j in a cell ito an access point j may be expressed as

H_(k)^([i, j]) ∈ C^(M × L).Each user terminal may estimate the channel matrix from a beacon packetor a sounding packet periodically transmitted from the access points.

An access point k generates an interference spaceQ_(k)=[q_(k,1),q_(k,2), . . . , q_(k,M−S)] for the IA based on a randomscheme. A null space of Q_(k) corresponding to a desired signal spacemay be expressed as shown below.U _(k) =[u _(k,1) ,u _(k,2) , . . . , u _(k,S)]=null(Q _(k))

A cell k may transmit Q_(k) and U_(k) to every station through a beaconand the like. Since Q_(k) and U_(k) are generated based on the randomscheme, Q_(k) and U_(k) may be influenced by values of M and S.

In operation 202, the frame transmission method of IA and controllingmay perform the SVD based on the calculated channel matrix and select abeamforming vector in consideration of an interference amount associatedwith another access point based on the

SVD performed in the channel matrix.

Each user terminal may calculate the beamforming vector of which theinterference amount associated with a desired signal space in anothercell is a minimum. A beamforming scheme in the foregoing example may bedescribed as shown below.

According to the frame transmission method of IA and controlling, achannel associated with desired signal spaces of other access points maybe preferentially expressed in a format of Equation 1 in order togenerate a beamforming vector

w^([i, j])(w^([i, j])² = 1)of a user terminal j in a cell i.

$\begin{matrix}{G^{\lbrack{i,j}\rbrack} = \begin{bmatrix}{( {U_{1}^{H}H_{1}^{\lbrack{i,j}\rbrack}} )^{T},\ldots\mspace{11mu},( {U_{i - 1}^{H}H_{t - 1}^{\lbrack{i,j}\rbrack}} )^{T},( {U_{i + 1}^{H}H_{t + 1}^{\lbrack{i,j}\rbrack}} )^{T},\ldots\mspace{11mu},} \\( {U_{K}^{H}H_{K}^{\lbrack{i,j}\rbrack}} )^{T}\end{bmatrix}^{T}} & \lbrack {{Equation}\mspace{14mu} 1} \rbrack\end{matrix}$

The frame transmission method of IA and controlling may calculate aformat of Equation 2 by performing the SVD with respect to G^([i,j]).G^([i,j])=Ω^([i,j])Σ^([i,j])V^([i,j])  [Equation 2]

In operation 203, the frame transmission method of IA and controllingmay select the beamforming vector in Equation 3 based on Equation 2.Concisely, the frame transmission method of the IA and controlling mayselect the beamforming vector of which the interference amountassociated with another access point is a minimum.

$\begin{matrix}{w_{SVD}^{\lbrack{i,j}\rbrack} = {{\arg\mspace{11mu}{\min\limits_{v}{{G^{\lbrack{i,j}\rbrack}v}}^{2}}} = v_{L}^{\lbrack{i,j}\rbrack}}} & \lbrack {{Equation}\mspace{14mu} 3} \rbrack\end{matrix}$

In operation 204, the frame transmission method of IA and controllingmay calculate a leakage interference (LIF) value based on the selectedbeamforming vector.

The frame transmission method of IA and controlling may calculate anamount of the LIF value defined by Equation 4 based on the beamformingvector through the user terminal.

$\begin{matrix}{\eta^{\lbrack{i,j}\rbrack} = {\sum\limits_{{k = 1},{k \neq i}}^{K}\;{{U_{k}^{H}H_{k}^{\lbrack{i,j}\rbrack}w^{\lbrack{i,j}\rbrack}}}^{2}}} & \lbrack {{Equation}\mspace{14mu} 4} \rbrack\end{matrix}$

The LIF value may represent a total amount of interference associatedwith another cell.

FIG. 3 is a flowchart illustrating a frame transmission method of IA andcontrolling through a backoff method for a channel access.

In operation 301, a channel may stand by until the channel is in an idlestate and backoff may be performed based on operations 302 through 306when the channel is in the idle state.

Concisely, the backoff method for the channel access may receive a CWvalue broadcasted by an access point and set a backoff counter based onthe received CW value. Also, an LIF value related to the access pointmonitored for a predetermined period of time may be generated and thebackoff may be performed by setting the backoff counter when the channelis in the idle state.

To perform the backoff, a range of cumulative distribution function(CDF) values may be divided based on the CW value and the LIF value maybe calculated based on a channel condition during a transmissionattempt. Also, the CDF values corresponding to the calculated LIF valuemay be calculated and the backoff counter may be selected based on thecalculated CDF values.

Access points may periodically broadcast the CW value and each userterminal may set the backoff counter between 0 and the CW value.

Each user terminal may monitor the LIF value related to other accesspoints in a long period of time and generate the related CDF.

Each user terminal may perform the backoff when the channel is in theidle state and the backoff counter may determine a value from 1 to theCW value based on a channel characteristic, for example, an LIF value.

Referring to FIG. 4, a frame transmission method of IA and controllingmay divide a range of CDF values based on a contention window value.

For example, FIG. 4 illustrates the CDF values associated with an LIFvalue and the CW value.

In operation 302, the frame transmission method of IA and controllingmay calculate the LIF value based on a channel condition during atransmission attempt and calculate the CDF values corresponding to thecalculated LIF value. In operation 303, the frame transmission method ofIA and controlling may calculate a backoff counter based on thecalculated LIF value.

In operation 304, the frame transmission method of IA and controllingmay perform backoff by decreasing the backoff counter by 1 for eachbackoff slot and attempting a packet transmission through a userterminal of which the backoff counter is to be 0.

Referring to FIG. 4, user terminals having small LIF values may setsmall backoff counters, thereby accessing channels.

In operation 306, the frame transmission method of IA and controllingmay determine whether a channel is accessed and transmits a packet whenthe channel is accessed.

When the channel is not accessed, the frame transmission method of IAand controlling may return to operation 301 and standby until thechannel is in an idle state.

Based on a backoff algorithm, simultaneous transmissions of the userterminals may be generated.

When packet transmissions fail to be performed for all user terminalsduring the simultaneous transmissions, all user terminals in the systemmay increase the CW value to be doubled and use the doubled CW valueduring a subsequent packet transmission attempt. When the CW valuereaches a predetermined maximum value, the increased CW value may bemaintained in lieu of an increase. When a packet transmission of apredetermined user terminal succeeds, an acknowledgement may bebroadcasted by a corresponding access point. Accordingly, all userterminals may read information associated with the foregoing descriptionand initiate the CW value as a predetermined minimum value.

Preferentially, when a channel is not occupied, the user terminal maycalculate the LIF value based on a channel condition. A process of thecalculation of the LIF value may include a beamforming based on an SVDon a physical layer. The backoff counter may be set based on thecalculated LIF value using the CW value and the CDF values correspondingto the LIF value. The backoff counter may decrease for each backoff slotand suspend the backoff when another user terminal attempts the packettransmission. When the packet transmission is not performed and thebackoff counter is 0, the user terminal may attempt the packettransmission and enter into a third stage.

The packet transmission may succeed or fail in response to interferencesfrom the user terminals to which the simultaneous transmissions are tobe directed.

The CW value for a channel access may be set.

The CW value is set at the access point based on a first throughputobtained from a packet that arrives in a desired signal space and asecond throughput to be obtained through a multiple-packet recoveryusing a user terminal performing simultaneous transmissions throughout asystem. The CW value is set as a constant based on a reciprocal value tomaximize a sum of the first throughput and the second throughput.

A case in which K cells coexist, each access point includes M antennas,and each user terminal includes L antennas may be considered.

Each cell may include N users and each access point may set a size of adesired signal space to correspond to S. When an interference amountfrom another cell is sufficiently small, the access point maytheoretically support simultaneous transmissions of users in a cell fora maximum of S users. A transmission probability p of the user terminalsmay be approximate to 1/CWmin, and a throughput corresponding to theforegoing description may be expressed as shown in Equation 1.

$\begin{matrix}{{Throughput} = {K\{ {\frac{\frac{\sum\limits_{n = 1}^{S}\;{{m\begin{pmatrix}N \\m\end{pmatrix}}{p^{\infty}( {1 - p} )}^{N - \infty}}}{{\sigma( {1 - p} )}^{KX}\mspace{11mu}\mspace{11mu}{T\lbrack {1 - ( {1 - p} )^{KX}} \rbrack}}}{\frac{\begin{matrix}{\sum\limits_{n = {S + 1}}^{N}\;{{m\begin{pmatrix}N \\m\end{pmatrix}}{{p^{\infty}( {1 - p} )}^{N - \infty} \cdot}}} \\\lbrack {\sum\limits_{i = 0}^{N - \infty}\;{\begin{pmatrix}{N( {K - 1} )} \\t\end{pmatrix}{p^{i}( {1 - p} )}^{{N{({K - 1})}} - 1}}} \rbrack\end{matrix}}{{\sigma( {1 - p} )}^{NK}\mspace{11mu}\;{T\lbrack {1 - ( {1 - p} )^{NK}} \rbrack}}} \div} \}}} & \lbrack {{Equation}\mspace{14mu} 5} \rbrack\end{matrix}$

In Equation 1, a first portion in the parentheses denotes a firstthroughput corresponding to the throughput obtained from the packet thatarrives in the desired signal space. The second portion in theparentheses denotes a second throughput corresponding to a throughput tobe obtained through a multiple-packet recovery since a number of usersperforming simultaneous transmissions throughout a system is less than anumber of antennas of access points. In Equation 5, a p_optimal value tomaximize a throughput may be preferentially calculated and the CW valuemay be calculated as a constant approximate to a reciprocal value1/p_optimal.

FIG. 5 is a flowchart illustrating a frame transmission method of IA andcontrolling through a stream reception method at an access point.

In a multi-cell network based on a random access, multiple users mayattempt simultaneous transmissions. An access point may verify whether auser attempting data transmission corresponds to a user in a cell of theaccess point, thereby differentiating a receiving method in response toa number of users attempting entire simultaneous transmissions.

The frame transmission method of IA and controlling describes areceiving method at an access point.

In operation 501, the frame transmission method of IA and controllingmay stand by until a channel is in an idle state.

In operation 502, the access point may preferentially detect a receivingsignal. In operation 503, the access point may restore data transmittedby the user in the cell of the access point in a desired signal space ofthe access point.

When a number of users attempting simultaneous transmissions indifferent cells is greater than a size of a desired signal space, datareception may fail. In such a case, when a number of attemptingsimultaneous transmissions in different cells is verified to be lessthan a number of antennas at the access point, reception may beperformed based on a multiple-packet receive scheme. Since a receptionof a BSS signal is not performed and a size of a desired signal space ofthe BSS increases, a multiple-packet reception (MPR) may be available.

The frame transmission method of IA and controlling may return tooperation 501 and stand by until the channel is in the idle state whenthe data reception succeeds in response to a result of determinationperformed in operation 504.

In operation 505, when the data reception fails in response to theresult of determination performed in operation 504, the frametransmission method of IA and controlling may further determine whetheranother BBS signal is detected.

When another BBS signal is detected, the frame transmission method of IAand controlling may return to operation 503 by decreasing a number ofthe MPR.

In operation 507, when another BBS signal is not detected, the frametransmission method of IA and controlling may perform the MPR.

When another BSS signal is detected, the data reception in the desiredsignal space fails such that the access point may perform an additionalMPR.

FIG. 6 is a block diagram illustrating a frame transmission system 600of IA and controlling using a beamforming based on an SVD.

The frame transmission system 600 of IA and controlling includes, forbeamforming based on an SVD, a calculator 610, a processor 620, and aselector 630.

The calculator 610 may calculate a channel matrix of a BSS by measuringchannel information between an access point and a user terminal

For example, the calculator 610 calculates a channel matrix by measuringchannel information including a sounding frame and a beacon frameperiodically transmitted to a user terminal from an access point. Also,the calculator 610 transmits desired signal space information includinga null space and interference space information randomly generated forIA to the user terminal through the sounding frame or the beacon frame,

In this example, the interference space is information associated withan interference space allowing interference from user terminals indifferent cells, and the desired signal space information is informationassociated with a space set by the access point to receive a signal.

The processor 620 performs the SVD based on the calculated channelmatrix and the selector 630 selects a beamforming vector inconsideration of an interference amount associated with another accesspoint based on the SVD performed by the channel matrix.

FIG. 7 is a block diagram illustrating a frame transmission system 700of IA and controlling using a backoff for a channel access

The frame transmission system 700 of IA and controlling includes, for abackoff for a channel access, a receiver 710, a setter 720, and aprocessor 730.

The receiver 710 receives a CW value broadcasted by an access point.

The setter 720 sets a backoff counter based on the received CW value.

The processor 730 generates an LIF value related to an access pointmonitored for a predetermined period of time and performs a backoff bysetting the backoff counter when a channel is in an idle state.

For example, the processor 730 divides a range of CDF values based onthe CW value, calculates the LIF value based on a channel conditionduring a transmission attempt, calculates the CDF values correspondingto the calculated LIF value, and selects the backoff counter based onthe calculated CDF values.

FIG. 8 is a block diagram illustrating a frame transmission system 800of IA and controlling using a stream reception at an access point.

The block diagram illustrating the frame transmission system 800 of IAand controlling includes, for a stream reception at an access point, acounter 810, a comparer 820, and a setter 830.

The counter 810 may verify a number of users performing simultaneoustransmissions in different cells.

The comparer 820 may compare the verified number of users to a number ofantennas at the access point.

The setter 830 may set, based on the result of the comparing, to receivea stream in a multiple-packet scheme when the number of antennas at theaccess point is less than the verified number of users.

The block diagram illustrating the frame transmission system 800 mayfurther include a determiner configured to determine whether multipleusers attempt the simultaneous transmissions. The counter 810 may verifythe number of users performing simultaneous transmissions in differentcells when the multiple users attempt the simultaneous transmissions.

Accordingly, an interference amount associated with access points incells of user terminals in a random access network may reduce therebyenhancing performance in multi-cell.

Also, to implement the IA scheme in an actual system, signaling overheadamong geometrically increasing nodes that may be needed. Therefore,technology for solving an issue of the need of the signaling overheadand maximizing a performance gain of the IA in a random access networkmay be required.

The above-described exemplary embodiments of the present invention maybe recorded in computer-readable media including program instructions toimplement various operations embodied by a computer. The media may alsoinclude, alone or in combination with the program instructions, datafiles, data structures, and the like. Examples of computer-readablemedia include magnetic media such as hard disks, floppy disks, andmagnetic tape; optical media such as CD ROM disks and DVDs;magneto-optical media such as floptical disks; and hardware devices thatare specially configured to store and perform program instructions, suchas read-only memory (ROM), random access memory (RAM), flash memory, andthe like. Examples of program instructions include both machine code,such as produced by a compiler, and files containing higher level codethat may be executed by the computer using an interpreter. The describedhardware devices may be configured to act as one or more softwaremodules in order to perform the operations of the above-describedexemplary embodiments of the present invention, or vice versa.

Although a few exemplary embodiments of the present invention have beenshown and described, the present invention is not limited to thedescribed exemplary embodiments. Instead, it would be appreciated bythose skilled in the art that changes may be made to these exemplaryembodiments without departing from the principles and spirit of theinvention, the scope of which is defined by the claims and theirequivalents.

What is claimed is:
 1. A frame transmission method of interferencealignment (IA) and controlling, the method comprising: receiving acontention window (CW) value broadcasted by an access point; setting abackoff counter based on the received CW value; and generating a leakageinterference (LIF) value related to an access point monitored for apredetermined period of time and performing a backoff by setting thebackoff counter when a channel is in an idle state, wherein the CW valueis set at the access point based on a first throughput obtained from apacket that arrives in a desired signal space and a second throughput tobe obtained through a multiple-packet recovery using a user terminalperforming simultaneous transmissions throughout a system.
 2. The methodof claim 1, wherein the performing of the backoff comprises: dividing arange of cumulative distribution function (CDF) values based on the CWvalue; calculating the LIF value based on a channel condition during atransmission attempt; calculating the CDF values corresponding to thecalculated LIF value; and selecting the backoff counter based on thecalculated CDF values, the backoff counter being selected according to achannel characteristic based on the LIF value.
 3. The method of claim 1,further comprising: decreasing the selected backoff counter by 1 foreach backoff slot and attempting a packet transmission through a userterminal of which the backoff counter is to be
 0. 4. The method of claim1, further comprising: decreasing the backoff counter for each backoffslot and suspending the backoff when a user terminal attempts a packettransmission.
 5. The method of claim 1, wherein the CW value is set as aconstant based on a reciprocal value to maximize a sum of the firstthroughput and the second throughput.